Fat continuous food products are well known in the art and include for example shortenings comprising a fat phase and water in oil spreads like margarine comprising a fat phase and an aqueous phase.
The fat phase of margarine and similar edible fat continuous spreads is often a mixture of liquid oil (i.e. fat that is liquid at ambient temperature) and fat which is solid at ambient temperatures. The solid fat, also called structuring fat or hardstock fat, serves to structure the fat phase (being the case in for example a shortening as well as in a water in oil emulsion) and helps to stabilize the aqueous phase, if present, by forming a fat crystal network. For a margarine or spread, ideally the structuring fat has such properties that it melts or dissolves at mouth temperature. Otherwise the product may have a heavy and/or waxy mouthfeel.
Important aspects of a fat continuous spread like for example margarine and low fat spread, the low fat spread usually comprising up to 45 wt % fat on total composition, are for example hardness, spreadability and ability to withstand temperature cycling.
Temperature cycling means that the product is subjected to low and high temperatures (e.g. when the consumer takes the product out of the refrigerator and leaves it for some time at the table prior to use). This may have a negative influence on the structure of the spread (like for example destabilization of the emulsion or oil-exudation).
Generally edible fat continuous food products like shortenings and margarines and similar edible fat continuous spreads are prepared according to prior art processes that encompass the following steps:    1. Mixing of the liquid oil, the structuring fat and if present the aqueous phase at a temperature at which the structuring fat is definitely liquid;    2. cooling of the mixture under high shear to induce crystallization of the structuring fat to create an emulsion;    3. formation of a fat crystal network to stabilize the resulting emulsion and give the product some degree of firmness;    4. modification of the crystal network to produce the desired firmness, confer plasticity and reduce the water droplet size.
These steps are usually conducted in a process that involves apparatus that allow heating, cooling and mechanical working of the ingredients, such as the churn process or the votator process. The churn process and the votator process are described in the Ullmans Encyclopedia, Fifth Edition, Volume A 16, pages 156-158.
A disadvantage of these processes is that the complete composition (including the liquid oil, structuring fat and if present the aqueous phase) is subjected to a heating step and a cooling step. This requires a lot of energy. For a spread comprising for example 6 wt % structuring fat the whole composition (100 wt %) has to be heated and cooled.
Another disadvantage of the known processes is that the choice of fats that can practically be used as structuring agent is rather limited. If the melting point of the structuring agent is too high the melting properties in the mouth are unsatisfactory. If on the other hand, the melting point is too low, the emulsion stability will be negatively affected. Moreover the amount of saturated fatty acids.
(SAFA) in the structuring agent is usually relatively high. Also trans fatty acid may be present. Some experts have called for reductions in these fatty acids to improve cardiovascular health.
Some consumers prefer spreads that have a low energy density (for example products that are low in total fat) and/or are low in SAFA but still have a good nutritional profile (by providing for example essential fatty acids like omega-3 and omega-6).
A further disadvantage of the known processes is that the product or ingredients may deteriorate due to the changes in temperature caused by the heating and cooling step.
Alternative processes have been described wherein the structuring fat is added as fat powder (i.e. crystallized fat) thereby eliminating the need to heat the whole composition to above the melting temperature of the structuring fat.
EP 1865786 A discloses a process for the preparation of a spreadable edible dispersion wherein a mixture of oil and solid structuring agent particles is subjected to stirring and an aqueous phase is gradually added to the mixture until a dispersion is obtained. The solid structuring agent particles have a microporous structure of submicron size particles and can be prepared using a micronisation process. The solid structuring agent particles (i.e. can be seen as fat powder) in such process need to be mixed with oil. Such can be achieved in various ways. Mixing powders of low bulk density (i.e. very fluffy powders) with a liquid, e.g. edible oil, can pose some difficulties.
When fat powder of structuring fat (e.g. of the kind as set out in the previous paragraph) needs to be mixed with liquid oil, e.g. in a ratio such that the oil/fat powder mixture contains about 2-40% (by weight) fat powder on the oil/fat powder combination, it was found to be advantageous to reduce the pressure to partial vacuum (e.g. 0.2 bar or lower) in the mixing vessel containing the powder, prior to or during the addition of oil and/or during the mixing thereof. The pressure is then raised to atmospheric pressure during or after the mixing. If such mixing is conducted well and the temperature of the oil is kept below the melting point of the structuring fat, the resulting product is a slurry of oil containing crystallized fat particles of the structuring fat.
Said slurry has a higher viscosity than the oil before it was mixed with the fat powder. In fact, during mixing the viscosity increases, as the fat powder is finely dispersed in the oil. Hence, viscosity builds as the fat powder is dispersed. It was found that when such slurry is to be mixed with an aqueous phase to produce a water in oil emulsion, slurries that perform well in the resulting emulsion (stability, firmness), should have a certain minimum viscosity. The process of making such slurry can take e.g. from 2 to 60 minutes. Clearly, it is desired that the required mixing time is as short as possible. Mixing (of oil and fat powder) time can depend on e.g. the type of equipment, the amount of powder over the oil, the type of oil and the type of fat used for the fat powder.
Still, despite the lowering of the pressure in the vessel in which the fat powder is contacted with the oil, in case the fat powder is a microporous fat powder as is e.g. described in J. of Supercritical Fluids 43 (2007) 181-190 and EP1651338 the mixing can cause difficulties.
Therefore, there is a need for an improved mixing process of mixing liquid oil with a microporous fat powder, in which viscosity builds sufficiently fast, or in other words: that mixing to yield a desired viscosity is achieved in a reduced amount of time.
US 2011/0287160 discloses a process for the preparation of low fat spreads comprising an emulsifier. The low fat spreads are made by mixing fat powder and oil, followed by mixing with an aqueous phase. At least part of the emulsifier is added through the aqueous phase.
US 2013/0192278 discloses a process for making fat powder by spray crystallization (or cryogenic spray process) for structuring oil-containing dispersions.